A traditional means that has been tried and found to be relatively good in collecting oil from water is a skimmer, i.e. a brush rotated partly in water and partly above the water, wherein the oil adheres to the bristles of the brush and is carried out of the water with the rotation of the brush. The bristles are then cleaned above the water by an appropriate comb structure before rolling once again back into the oily water. A structure based on bristles may be formed by one drum-type brush or alternatively by a brush cassette wherein a belt provided with bristles circulates between two rotating rolls.
However, problems are caused in the prior art by the operation of the brushes particularly in icy oil. Bits of ice are easily caught between radially extending bristles but are not adhered to the bristles; instead, they slip out, bringing along the oil adhered to the bristles. Furthermore, the oil retention capacity of the bristles is not fully satisfactory because the mere centrifugal force of rotation tends to draw oil away from the surfaces of the radial bristles. Thus, the rotational speed of the brushes must be kept quite low so as to prevent back flow of the oil.